Hydraulic fracturing -- the technique used on this gas pad in Pennsylvania -- involves lots of water. And that water comes in three varieties: fracking fluid, flowback water, and produced water. Is any of it safe?

When it comes to water from hydrofracking, the question of safety is murky at best.

Even so, many argue that the stuff may not be that bad — the fluid is injected well below the surface and unlikely to migrate to aquifers and surface water. They may have a point. A recent study by a Duke team — with an admittedly large caveat because it “did not test comprehensively for organics or other potential additives in fracking fluids” — found no evidence of fracking fluids in drinking water near well sites — although they did find methane contamination. The Environmental Protection Agency, however, as reported in the New York Times, has investigated at least one documented case of fracking fluid contamination.

Whatever problem fracking fluid might have posed in the past may become moot, as gas-drilling companies become more transparent and clean up their act. But even Halliburton’s newly formulated not-quite-“edible”-but-apparently-safe-to-drink fracking fluid doesn’t mean that all is hunky-dory in fracking water land. Why? Because there’s also flowback water and produced water.

Flowback Water

After water is introduced during the fracking stage, a portion of that is returned to the surface over the next days and weeks. The volume of this flowback water can range from as little as 10 percent [pdf] to as much as 100 percent of the fracking fluid. Initially, its composition resembles that of the injected fracking fluids, but as its residence time increases, its chemistry transitions to the composition of formation water found naturally within the shale, and once this change occurs, this water is called produced.

Produced Water

For a typical well, daily produced water volumes range [pdf] from about 80 to 1,200 gallons and are generated in tandem with shale gas over the well’s life. A lot of water and a lot of potential problems. Its composition is determined by the chemistry of the shale from whence it came. If there are toxic elements in the formation, there are likely to be toxic elements in the produced water.

Avner Vengosh, my colleague here at Duke’s Nicholas School, and his research group have been spending time in Pennsylvania gathering inorganic data specific to the Marcellus Formation. The table below shows some of their preliminary data for selected compounds collected over the first 20 days of a well operation. (Learn more about the study and its findings in this video.)

As you can see, the produced water in Avner’s samples was highly saline with a number of toxic trace elements, which far exceeded (up to a 1,000 times) what’s found in both drinking water and surface water ecological criteria; it also contained radium, a radioactive element.

Where It Goes Is What You Need to Know

For fracking to be safe water-wise, you gotta dispose of flowback and produced water without allowing it to mix with surface or drinking water. One method is injecting the stuff in deep geologic formations — however, there’s some evidence that such practices may lead to earthquakes, albeit small ones. Recycling the water, which preserves the local water supply and helps minimize the amount that must be disposed of, can have its own drawbacks — recycling creates a highly concentrated sludge which is often unregulated and without proper disposal can pose a risk to drinking water.

More problematic is the transfer of wastewater to water treatment facilities, most of which are ill-equipped to deal with the toxics and will therefore pass them on into rivers and potentially downstream drinking water supplies. (See here, here and here.)